Colloquium # 300

Relativistic charge solitons caused due to Nonlinear Landau Damping:
An excellent candidate for explaining the Coherent Radio Emission from

By Dr.Dipanjan Mitra

Tuesday, Jan 21st 2020 at 3:30 PM
Seminar Hall

Collective plasma emissions in astrophysics are referred to as coherent emission. Radio emission from Pulsar is an excellent example of coherent emission. Observations suggest that the radio emission is excited by accelerating "charge bunches'' formed in a relativistically streaming one dimensional pair plasma. These charge bunches moving along curved magnetic field lines excites curvature radiation in the plasma, which eventually escapes from the plasma and reaches the observer. Theoretically, it is challenging to form a stable charge bunch, yet they seem to be exist, and even after fifty years of pulsar discovery the mechansim of how collective plasma process excites the coherent radio emission remains an unresolved problem.

A potential resolution for the formation of charge bunches, is based on the classic problem of self-consistent linear and non-linear growth (or damping) of electrostatic Langmuir wave in collisionless plasma. In this talk I will show the application of the theory of linear/nonlinear growth of Langmuir wave in pulsar plasma. In the nonlinear regime, I will demonstrate the existence of stable relativistic charge solitons (the “charge bunches”) as solutions of the non-linear Schrodinger equation (NLSE). The formalism includes the crucial effect of nonlinear Landau damping, which is inherent in the derivation of the NLSE. I will also demonstrate a remarkable finding, i.e. the emergence of these intense soliton-like pulses from an initial disordered state of Langmuir waves.

The mechanism presented here has potential for wider application in understanding coherent radio emission phenomenon in astrophysics like in the Fast Radio Bursts.

About the speaker

Joined NCRA, TIFR in 2004 and Currently Associate Prof at National Centre for Radio Astrophysics, TIFR
Post Doctoral Position, Max-Planck Institut fur radioastronomie, Bonn, Germany, from February 2001 to January 2004. PHD on Pulsar Astrophysics from Raman Research Institute Bangalore, 2000. Held visiting positions for a year or longer: Arecibo Observatory Cornell Univeristy USA and University of Vermont USA. Work primarily on Radio Astronomy and Neutron star Astrophysics: Theory and Observations. Made contribution in establishing the emission mechanism being excited by curvature radiation in pulsars, and involved in developing a complete theory of coherent radio emission from relativistic plasma from first principles.